1. Field of the Invention
The invention concerns a magnetic rotary encoder which, for the fine resolution of the rotational angle of a shaft, has an exciter unit which images the rotation to be monitored and in that case rotates about an axis of rotation, a stationary fine resolution sensor unit for fine resolution of each revolution, and an electronic processing means.
2. Description of Related Art
EP 1 243 891 B1 proposes a rotary encoder having an actuating element in the form of a permanent magnet providing the magnetic fields required for absolute measurement of the fine position value, as is effected by means of a four-quadrant Hall probe whose Hall elements are connected in crossed relationship. In that respect amplitude and homogeneity of the magnetic field play an important part.
If a single two-pole permanent magnet is used in that connection, that results in the disadvantage that such an arrangement only allows the use of the return or so-called leakage fields of the permanent magnet, which are neither homogenous nor particularly strong nor are they in a linear relationship with the rotational angle. In particular the low field strength of the leakage fields used is found to be a handicap because weak fields require a high level of electrical amplification and thus lead to increased noise. In that case susceptibility to interference fields from the exterior and internal disturbance increase with falling field strength.